Hydrogen Fluoride-Catalyzed Addition of Carbon Monoxide to Propylene Under High Pressures*

Hydrogen Fluoride-Catalyzed Addition of Carbon Monoxide to Propylene under High Pressures*

Yoshimasa Takezaki**, Yoshio Fuchigami**, Hiroshi Teranishi**, Nobuyuki Sugita** and Kiyoshi Kudo**

Summary: Isobutyric acid forming reaction of propylene with carbon monoxide has been studied in the presence of HF-H2O catalyst under high pressures. The optimum conditions for the formation of acid have been decided as follows: water content of HF catalyst, 20 wt. %; charge ratio of HF to C3H6, 15 (mole ratio);reaction temperature,94℃ or lower;and the total pressure,190kg/cm2 or higher. Reaction temperature higher than 94℃ is unfavorable because of accelerated polymerization of C3H6. Reaction mechanism of the formation of isobutyric acid has been proposed, where the rate determining step,

C3H7++CO(dissolved)→C3H7CO+, being first-order with regard to each reactant. The rate expression for the yield of the acid has been derived and the apparent activation energy of the over-all reaction has been found to be 21.7kcal/mole.

Introduction

Since 1933 when several patents1) on the production of carboxylic acids from olefins and carbon monoxide in acidic media were In these works Koch obtained good yield published, many works have been carried (better than 90%) of acids when butene or out2)-22)on this process. On propylene as an higher olefin was used8),9), but in the case of olefin, the first systematic study was reported propylene5), detailed data on experimental by Hardy in 19362), in which the author, conditions and yields were not reported except using 87 %-phosphoric acid as the catalyst, for the formations of alcohols, esters and observed 50% yield of total acids (isobutyric carboxylic acids as the products. Such pro- acid and higher acids)at 200℃ and 200 atm ducts as alcohols and esters are elucidated of carbon monoxide pressure. After 1955, to be formed as follows15): Koch and his co-workers have shown that R++HOH⇔ROH+H+, olefins react rapidly with carbon monoxide RCO++ROH⇔RCOOR+H+. at room temperature and under moderate Recently Friedman and Cotton14)～16)con- pressures in the presence of catalysts such firmed Koch's indication that anhydrous as concentrated sulfuric acid3)～8), phosphoric hydrogen fluoride is a powerful catalyst for acid9), anhydrous hydrogen fluoride5),8), mono- olefin-carbon monoxide reactions. However hydroxyfluoboric acid and its mixtures with they found that relatively minor amounts of phosphoric or sulfuric acid10) or aqueous water in the catalyst affect the reaction and BF311),12), and Koch has suggested the fol- the nature of the products obtained, so by lowing mechanism13),23): controlling water content in the catalyst they succeeded in obtaining fairly good yields of carboxylic acids, and for propylene they re-

ported about 60%yield of acid at 75～100℃

* Received November 15 and 40 atm of carbon monoxide pressure . , 1965 ** Institute for Chemical Research In the present paper we wish to report , Kyoto University, Sakyo-ku, Kyoto. on the study carried out with the purposes

Volume 8-June 1966 32 Takezaki, Fuchigami, Teranishi, Sugita and Kudo: Hydrogen Fluoride- to find the optimum conditions for isobutyric determined from the weight decrease of the acid formation in the hydrogen fluoride- weighing vessel and that of the latter from catalyzed reaction of propylene and carbon the pressure decrease of the reservoir. As monoxide under high pressures and to eluci- soon as the charging of carbon monoxide was date mechanism of the reaction from kinetic finished, the stirrer was started and that viewpoint. instant was defined as the zero-time of reaction. In the case of isobaric measurement, Experimental carbon monoxide gas was supplied almost Apparatus continuously so as to keep the total pressure The experimental apparatus consisted of constant at the desired point. an autoclave, a weighing vessel for propylene, After reaction, the solution in the auto- a reservoir of carbon monoxide (500ml in clave was poured on ice-water and extracted capacity) and Bourdon-type pressure gauges with n-hexane. The organic acids contained which was previously calibrated by a dead- in the hexane and water layers were analyzed weight pressure gauge. The autoclave, made respectively ; the quantity of total organic of stainless steel (50mm in inner diameter and acids in each layer was determined by alkali 328ml in capacity), had a magnetic stirrer titration and mole ratios among acids by gas and the rotating speed of the stirrer was chromatography. In the analysis of water watched by means of a stroboscope and layer, the solution was neutralized with NaOH controlled withinｱ50 r. p. m. The autoclave at first, then after drying the organic salts was heated by an electric furnace and the were extracted by methanol from NaF. The temperature of the vessel was maintained at methanol solution was dried again and the each experimental temperature withinｱ1.0℃ sodium salts of acids were dissolved in water, measured by a chromel alumel thermocouple and, after converting to free acids by ion- inserted in the hole bored in the wall of exchange resin the trace of HF remaining vessel. in the solution was removed off as CaF2. Materials Carbon monoxide was prepared by adding Results and Discussion formic acid to hot concentrated sulfuric acid, Preliminary experiments washed with aqueous caustic soda and com- In order to identify the products and to pressed into the reservoir up to about 300 find the optimum conditions for kinetic kg/cm2. The purity of the gas used was 97% measurements of the reaction, some pre- as determined by gas chromatography and liminary runs were carried out. the greater part of the impurity was air. 1) Identification of products : The organic Propylene was prepared by dehydration of acids produced were, as would be expected isopropyl alcohol through activated alumina from the results of previous investigators, at 375～400℃, and dried with CaCl2. The monocarboxylic acids of C4 as the major part crude propylene was purified by bulb-to-bulb and those of C7 as the remainder (hereafter distillation under vacuum. The purity was designated C4-acid and C7-acid, respectively). 99.97% as determined by gas chromatography. Carboxylic acids higher than C7 were not HF gas was obtained from Daikin Kogyo detected. Although in the products of the Co. Ltd. and the purity was determined to run under more severe conditions some be 99.5% by electric conductivity measure- amounts of dark brown oily matter were ment. obtained, which resulted from polymerization Procedure of propylene and might contain some kinds The weighed amount of HF-H2O mixture of higher acids. In the usual case of present at a desired mixing ratio was sucked into experiment such coloration were scarcely the pre-evacuated autoclave. After the auto- observed. clave attained an experimental temperature, As shown in Table 1, the C4-acid and C7- propylene and carbon monoxide were charged acids were identified to be isobutyric acid and into it, and the amount of the former was α-,γ-dimethylvaleric acid respectively from

Bulletin of The Japan Petroleum Institute Catalyzed Addition of Carbon Monoxide to Propylene under High Pressures 33

Table 1. Identification of acids produced

their boiling points, refractive indices, ele- mental analyses, molecular weights, gas chromatographies and infrared spectra. The C7-acid could not be identified by the infrared spectrum because of the lack of data on α-,

γ-dimethylvaleric acid to be compared, but the absorption peaks observed could be regarded as characteristic ones to monocarboxylic acids. Other isomers of C4- and Fig. 2-a Relation between water content of HF C7-acids were not detected by gas chroma- catalyst and yield of acids tography. 2) Reaction temperature: The relations between reaction temperature and the yield of total acids obtained when other conditions were fixed, are shown in Fig. 1. The curve shows the maximum yield at 94℃ and above this temperature the polymerization of propylene becomes pronounced as evidenced by the dark color of product solution. Fig. 2-b Relation between water content of HF catalyst and time spent for completion of reaction

The curve shows the maximum yield at about

20wt. % water, but in the region of 13～

20%the differences among the yields are only

10～15%. On the other hand, the water content shows much more remarkable effect on the reaction speed; as shown in Fig. 2-b, Fig. 1 Relation between temperature and yield of acids as to propylene charged the time spent for completion of reaction (defined by the time until the pressure de- 3) Water content of HF catalyst: The crease stops) is much prolonged with the effect of water content of HF catalyst on increase of water content. In these runs the the yield of total acids is shown in Fig. 2-a. mole ratio, HF/C3H6, was fixed at 5.0ｱ0.2.

Volume 8-June 1966 34 Takezaki, Fuchigami, Teranishi, Sugita and Kudo: Hydrogen Fluoride-

hence the water content 15wt.% corre- yields of acids, after the same duration in sponds to H2O/C3H6=1 and this ratio becomes both cases, coincided with each other within smaller with the decrease of water content. the accuracy of analysis. In another run, From stoichiometry of the acid forming reac- the speed was changed several times during tion, the condition such that the H2O/C3H6 the reaction but no discontinuity was observed ratio is smaller than 1 is unfavorable for on the curve of CO absorption. These results our purpose and C3H6 in excess of the stoi- suggest that the diffusion process can not be chiometry may be consumed by polymerization the rate-determining step if the speed is reaction. As shown in Figs. 2-a and 2-b, more than 600 r.p.m. under the present ex- the decreasing tendency of the acids yield perimental conditions. in the reactions at water contents of less Kinetic measurements than 15wt.% seems to coincide with this From the results described above, following situation. This fact also would elucidate the conditions have been adopted as the optimum reason why Friedman and Cotton used HF- throughout the runs for kinetic measurement: H2O catalysts instead of anhydrous HF as HF/C3H6 in mole ratio: 15.0, suggested by Koch. water content of HF catalyst: 20.0wt.% 4) Charge ratio of HF to C3H6: The rotation of stirrer: 1000 r.p.m. results of the experiments where the charge and reaction temperature: lower than 94℃. ratio of HF to C3H6 was changed are shown 1) Effect of CO pressure: The kinetic in Fig. 3. As the water content of the measurements were carried out at 88℃ and total pressures of 50, 100 and 190kg/cm2. The experimental conditions and results obtained are listed in Table 2 and shown in Fig. 4. In these runs the partial pressure

Fig. 3 Relation between HF/C3H6 and yield of acids

catalyst is fixed at 20wt. %, the change in the mole ratio, HF/C3H6, from 5 to 15 corresponds to that of H2O/C3H6 ratio from 1.4 to 4.1 respectively. The yields are better than 96% when the HF/C3H6 is 14 or higher, but in the range lower than this, the larger concentration of dissolved C3H6 in the HF- H2O solution results in the meager yield of Fig. 4 Effect of pressure on the rate acids; this would be elucidated if we assume of acid formation that the acid forming reaction is first-order as to the concentration of C3H6, and the of C3H6 decreases as the reaction proceeds, polymerization is second or higher order as so, strictly speaking, the partial pressure of to C3H6 concentration. CO, Pco, can not be constant even though CO 5) Effect of stirring: In order to check is supplied in order to maintain the total the effect of stirring on the reaction velocity, pressure constant. However, since the partial two runs were carried out under one fixed pressure of C3H6 was about 5kg/cm2 at the condition (HF/C3H6 is 15.0 in mole ratio; initial stage, the deviations of pco from its water content of HF catalyst, 20wt. %; initial values were at most only 3～4%, so reaction temperature,92℃ and total pressure, the effect on the yield of acids due to such 116kg/cm2) except for the speed of the deviation would be negligible. As shown in magnetic stirrer, 600 and 1500 r.p.m. The Fig. 4, the formation of the C4-acid is

Bulletin of The Japan Petroleum Institute Catalyzed Addition of Carbon Monoxide to Propylene under High Pressures 35

Table 2. Conditions and results of the yield only to one half. kinetic measurements Reaction mechanism and rate equation Formation of carboxylic acid from C3H6 and CO in HF-H2O medium must begin with the primary reaction of dissolved propylene, C3H6(d), with hydronium ion, H3O+,

The propyl cation, C3H+7, thus formed will combine with dissolved carbon monoxide, CO(d), accelerated as the pco increases. It should be noticed that when the total pressure, P, is 190kg/cm2 the yield of C7-acid attains a Then the reaction will be completed by ad- constant value after about 10 minutes, and dition of water, when P is 100kg/cm2 the yield becomes C3H7CO++H2O→C3H7COOH+H+. (3) constant at about twice as large as that of As side reactions, following steps may be the former case after a reaction duration conceivable to elucidate the formation of twice as long, so, at 50kg/cm2 still larger C7-acid or polymers: yield may be expected after still longer time. 2) Effect of temperature: The effects of temperature on the reaction velocity were examined at 88,68 and 50℃, and the results are shown in Table 2 and Fig. 5. When the

In deriving the rate equation for the C4- acid forming reaction, we assume: 1. Reactions (1) are at equilibrium throughout the whole reaction time Fig. 5. Effect of temperature on the rate with the equiliblium constants K1 and of acid formation K2 respectively. reaction temperature is lowered from 88 to 2. C3H6(d) and CO(d) are at equilibrium 68℃, the yield of C7-acid is decreased to one with partial pressures of respective tenth. This remarkable effect of temperature gases with Henry's constants Hp and on the yield of C7-acid is of interest as HCO. compared with the fact that the pressure 3. Reaction (2) is the second-order re- increase from 100 to 190kg/cm2 depresses action, that is, first order as to each

Volume 8-June 1966 36 Takezaki, Fuchigami, Teranishi, Sugita and Kudo: Hydrogen Fluoride-

reactant and this step is rate deter- where y=n4/n0, the yield of C4-acid as to mining in the whole reaction. C3H6 charged

The vapor pressure of C3H6 has been re- z=2n7/n0, the yield of C7-acid as to ported as 20 atm at 50℃ and 45 atm at C3H6 charged, 90℃25) and in the present work the partial and k'=AkHco. pressure of C3H6 is at most 5 atm, so no Because of the decrease of w during the liquid propylene would take part in the reaction, A is not constant; however, the reaction. maximum consumption of H2O in the present For C3H6 and CO, Henry's law shows work has been estimated to be 23% of the initial quantity and corresponds to the increase fp≒Pp=nlp/HpVt (4) of A at most by 14%. Since we are mainly and fCO=nlCO/HCOVl, (5) to deal with the initial rate, A may be re- where fp and fCO are fugacities of C3H6(g) garded as constant, and so for k', too. From Eq. (11), the initial rate of the C4- and CO(g), Pp is the partial pressure to acid formation is written as C3H6, nlp and nlCO the moles of C3H6(d) and CO(d) and Vl the volume of the solution. Since Reactions (1) are at equilibrium, the moles of C3H7+, x, is given as where k'0 is the k' at t=0. As described above, z, the yield of C7-acid, attains a small constant value for each condition. If z can be regarded as constant from the beginning where h and w are moles of HF and H2O in of the reaction, Eq. (11) can be integrated the solution respectively. From the state equation of C3H6(g) and as the material balance of propylene. we have -log(1-y-z')=ct , (13) ngP=Pp(V-Vl)/RT, (7) where c=const.=k'fCO/2.303 and z'=const. and n0=ngp+nlp+x+n4+2n7, (8) The curves for the yields of C4-acid shown in Fig. 4 are best fitted by the following where V is the whole capacity of reaction equations: vessel, R gas constant and n0, ngp, n4 and n7 at 190kg/cm2 moles of total propylene, C3H6(g), C4-acid and y=5.40×10-2t-9.20×10-4t2

C7-acid respectively. (within±2%fort=0～30min.) Eqs. (4), (6), (7) and (8), lead to at 100kg/cm2

y=2.63×10-2t-3.25×10-4t2 (withinｱ2% for t=0～40min.) and at 50kg/cm2 where y=1.25×10-2t-1.37×10-4t2

(within±1% for t=0～40min.) In Fig. 6, the values of (dy/dt)t=0 obtained by differentiating these equations are plotted

Since Reaction (2) is assumed to be first- order as to each reactant, the rate equation becomes

where k is the rate constant of Reaction (2). Substituting Eqs. (6) and (9) in (10), we have

Fig. 6 Relation between initial rate and fugacity of CO

Bulletin of The Japan Petroleum Institute Catalyzed Addition of Carbon Monoxide to Propylene under High Pressures 37 against fCOoestimated by graphical integra- at 88℃ y=5.40×10-2t-9.20×10-4t2 tion27) using the published P-V-T data of CO26), (within 2%for t=0～30min.) and the plots show a good straight line as at 68℃ y=1.08×10-2t-1.13×10-4t2 expected from Eq. (11). This gives an evi- (within 1%for t=0～40min.) dence for the assumption that Reaction (2) and at 50℃ y=0.225×10-2t. is first-order as to CO(d) concentration. From Table 3. Effect of temperature on the initial rate the slope of the line, we have of isobutyric acid formation

k'0=2.94×10-4min-1atm-1(at 88℃). (14) For examination of Eq. (13), the results of runs R67, R68 and R69 are suitable because the partial pressures of CO are within the range 184.5～187kg/cm2 throughout

these runs, that is, fCO can be regarded as * Unit: min-1 atm-1

constant at 189ｱ1.3 atm., moreover the yield, y, shows large increase from 45% to 90% during the time interval of 10 to 40 minutes. The values of log (1-y-z') calculated are plotted against time in Fig. 7 and they show

Fig. 8 Arrhenius plot of k'0 Fig. 7 Relation between log (1-y-z') and time The results are listed in Table 3 and the a good straight line. Therefore, the as- Arrhenius plot in Fig. 8. From the slope sumption that A is constant seems to be the apparent activation energy for over-all approvable even when moles of water, w, reaction is determined as 21.7 kcal/mole. change by about 10%. Extrapolation of the log k'0, the ordinate of Fig. 8 is written as line in Fig. 7 goes through the origin; this fact is rather accidental, because in the initial stage of reaction, z is not constant but increases with time, hence Eq. (13) can not be used in this region. The value of k' calculated from the slope of line in Fig. 7 is, hence, it can be deduced from the linearity of the Arrhenius plot that the temperature k'=3.53×10-4min-1atm-1(at 88℃). (15) dependence of the second term is negligibly The difference between this value and that small as compared with that of the first of Eq. (14) is about 20%, but the difference term in the present temperature region. of such order of magnitude may be allow- able since z is not exactly constant and w Conclusions decreases rather rapidly in the initial stage The mechanism of isobutyric acid forming of the reaction. reaction of propylene with carbon monoxide The values of initial rate constant under in the presence of HF-H2O catalyst has been various temperatures have been determined proposed to consist of Reactions (1), (2) and by differentiation of next equations, which (3). The rate determining step has been fit the curves in Fig. 5: decided as Reaction (2), that is the second-

Volume 8-June 1966 38 Takezaki, Fuchigami, Teranishi, Sugita and Kudo

order reaction of propyl cation, C3H7+, with 10) Koch, H., Huisken, W., U.S. 2,876,241 (1959). carbon monoxide dissolved in the solution. 11) Koch, H., Haaf, W., Ann. der Chem., 638, 111 (1960). The rate expression for the isobutyric acid 12) Koch, H., Ger. 1,095,802 (1962). formation has been derived as Eqs. (12) and 13) Koch, H., Fette vnd Seifen, 59, 493 (1957). (13), and the rate constants and the apparent 14) Friedman, B. S., Cotton, S. M., U.S. 2,975,199 activation energy have been determined. (1961). 15) Friedman, B. S., Cotton, S. M., J. Org. Chem., The maximum yield of isobutyric acid, 97% 26, 3751 (1961). as to propylene charged, has been obtained 16) Friedman, B. S., Cotton, S. M., J. Org. Chem., under such conditions that water content of 27, 481 (1962). HF catalyst is 20wt.%, mole ratio of HF 17) Shell International Research, Brit. 883,142 (1959). 18) Waale, M. J., Vos, J. M., Neth. Pat., 100,296 (1962). to C3H6 15, reaction temperature 94℃ and 19) Vos, J. M., de Vries, R., U.S. 3,059,007 (1962). the total pressure 190kg/cm2. And under 20) Vos, J. M., de Vries, R., Brit. 934,818 (1963). higher pressures of carbon monoxide, better 21) van Dam, J., Waale, M. J., Chim. Ind. (Paris), yields of isobutyric acid would be expected 90, 511 (1963). with good selectivity. 22) Roming, C. Jr., U.S. 3,068,256 (1962). 23) Meinwald, J. E., Hwang, H. C., Christman, D., Wolf, A. P., J. Am. Chem. Soc., 82, 484 (1960). References 24) Cason, J., Harris, E. R., J. Org. Chem., 24, 676 1) Carpenter, G. B., U.S. 1,924, 762-8 (1933). (1959). 2) Hardy, D. V. N., J. Chem. Soc., 364 (1936). 25) Marchman, H., Pringle, H. W., Motard, R. L., 3) Koch, H., Brennstoff-Chem., 36, 321 (1955). Ind. Eng. Chem., 41, 2658 (1949); Jordan, T. E., "Vapor pressure of Organic Compounds" 4) Koch, H., Rev dei Combustibili, 10, 77 (1956). , P. 3, 7 5) Koch, H., Belg. 518,682 (1955); Brit. 743,597 (1957); (1954), Intersci. Pub. Inc., New York. U.S. 2,831,877 (1958). 26) Michels, A., Lunbeck, R. L., Wolkers, G. J., Appl. 6) Koch, H., Haaf, W., Angew. Chem., 70, 311 (1958). Sci. Res., A2, 345 (1951); Din, F., "Thermo- 7) Koch, H., Haaf, W., Ann. der Chem., 618, 251 dynamic Functions of Gases", Vol. 1, P. 175 (1956) (1958). Butterworths Sci. Pub., London. 8) Koch, H., Ger. 972,315 (1961). 27) Comings, E. W., "High Pressure Technology", P. 9) Koch, H., U.S. 3,061,621 (1963). 267 (1956). McGraw-Hill Book Co. Inc., New York.

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